Add final_pos/vel props for primaries and secondaries

[TomWagg]

This pull request introduces new convenience properties to the Population class for easier access to the final positions and velocities of primary and secondary stars, updates related documentation and tests, and bumps the package version. These changes improve usability and make analysis more straightforward.

Enhancements to the Population class:

• Added final_primary_pos, final_secondary_pos, final_primary_vel, and final_secondary_vel properties to the Population class in cogsworth/pop.py. These properties provide direct access to the final positions and velocities of primary and secondary stars as numpy arrays, handling both regular and disrupted binaries. [1] [2]

Testing improvements:

• Added a new test test_primary_secondary_pos_vel in cogsworth/tests/test_pop.py to verify the correctness of the new properties for both positions and velocities.

Documentation updates:

• Documented the new properties and their purpose in the changelog (docs/modules/changelog.rst).
• Updated installation instructions to recommend Python 3.11 instead of 3.10 in docs/pages/install.rst. [1] [2]

Version update:

• Bumped the package version to 3.6.2 in cogsworth/_version.py.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b184276) to head (7397deb).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Lines         2238      2254   +16     
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+ Hits          2238      2254   +16     

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